Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

The posterior epithelium is the anterior extension of non pigmented epithelium of ciliary body and merges with the anterior epithelial layer.

The pigment epithelium acts as blood aqueous barrier besides preventing light from entering the eye.

The pupil

The pupil is not a tissue, it is a deficiency in the iris. It is circular in shape, situated in the center and slightly nasally in the iris. The periphery of the pupil is black in colour due to posterior pigment epithelium of the iris spilling anteriorly. This is called ruff of the iris. The size of a normal adult pupil is 2 mm. to 4 mm. It is smaller in new born and in old age. Pupil smaller than normal is called miotic pupil, while larger than the normal is called mydriatic pupil. The drugs that constrict the pupil are called miotics, while those that dilate are called mydriatics. Generally the size of the pupil is equal in the two eyes. Difference in the sizes of the pupil in two eyes is called anisocoria. Presence of more than one pupil in each eye is called polycoria, which is a congenital condition. Pupil in true polycoria should have independent sphincter and dilator muscles. Pseudopolycoria can be seen as congenital anomaly i.e. dysgenesis of anterior chamber or may be acquired following trauma which is mostly surgical or may be accidental. In some chronic uveitis, there may be loss of iris tissue resulting in holes in the iris. A deficiency in iris is called coloboma that can be congenital or acquired. It is very common for the coloboma of the iris to extend up to pupil resulting in a vertically enlarged key hole shaped pupil. Such pupil are capable of reacting to light and accommodation to a limited extent. Corectopia is a term used to denote the position of the pupil other than normal, this is generally bilateral and congenital.

Normally the pupil is never stationary and its size keeps on changing within a normal range, with change of intensity of light and accommodation. An appreciable flicker of pupil is called hippus, which is of no clinical significance.

The function of the pupil is to control the light entering the eye. It acts as communication between anterior and posterior chamber through which aqueous passes from the posterior chamber to the anterior chamber.

The ciliary body

This is the middle part of the uvea. It extends from scleral spur anteriorly, to ora serrata posteriorly. It encircles the interior of the sclera. In section it looks like an isosceles triangle, the base of which points towards the pupil. The outer edge of the base is attached to the scleral spur, 1.5 mm. away from the limbus. From the middle of the base arises the iris dividing the base into two parts, the anterior part forming the angle of the anterior chamber. This part is visible on gonioscopy only. The posterior part forms the boundary of the posterior chamber.

The ciliary body is highly vascular and bleeds profusely on trauma, both blunt and penetrating.

It’s colour is brownish black. The ciliary body is empirically divided into two parts:

1. Pars plicata. The Pars plicata is anterior 2 mm. of the ciliary body. This is the thickest part of the uvea. It comprises of ciliary stroma, ciliary muscles, blood vessels and nerves. The inner surface of para plicata is divided into 70 to 80 ridges or plications. These are known as ciliary processes, they extend towards the lens, in finger like processes. Each of them is 0.5 mm. x 2.00 mm. in size. From the tips of these processes arise the zonules of the lens. The lens and the zonules together form a barrier that separates the vitreous chamber from the aqueous chamber. The ciliary processes are made up of capillaries covered by two layers of ciliary epithelium. They do not have any stroma or muscles, their length depends on tightness of the ciliary muscles3. Besides acting as attachment of zonules, that are responsible for accommodation, the other function of the ciliary process is to secrete aqueous.

The ciliary epithelium acts a blood aqueous barrier. The non-pigment epithelium secretes aqueous while the pigment epithelium continues as retinal pigment epithelium.

2. Pars plana. The pars plana is posterior 6 to 7 mm. of the ciliary body. This gradually looses its musculature and tappers as a thin layer to end in ora serrata that ultimately blends with the choroid and the retina. The vascular layer of the pars plana is similar to that of choroid without choriocapillaries. The vitreous base extends from retinal periphery up to 2 mm. of pars plana. The pars plana is thought to secrete mucopolysaccharides of the vitreous.6 The pars plana being less vascular than any other part of the uvea with minimum thickness is the natural choice of entry for intra vitrial surgery and lensectomy.

The ciliary muscles form the main bulk of the ciliary body. The muscles are nonstriated muscles that has three parts. The most important are the longitudinal fibres. The middle part is formed by the radial fibres. While the innermost are the circular fibres. Most of the bulk of the ciliary muscle is located in the anterior two-third of the ciliary body. The exact function of the ciliary muscles are not well understood, however, the ciliary muscles take a major part in accommodation. Contraction of the ciliary muscles open up the angle of the anterior chamber to facilitate aqueous out flow.

The nerve supply of the ciliary body is mostly by parasympathetic nerve. Sympathetic supply has lesser role to play in the ciliary body. The sensory supply is via trigeminal.

The choroid

The choroid is the posterior most part of the uvea and forms a major part of the middle layer of the coats of the eyeball. It extends from optic nerve to the ora serrata between the sclera on the outer side and retina on the inner side. It is continuous with ora serrata anteriorly with loose attachment to the 1. The sclera, 2. The exit of the vortex veins near the equator, 3. round the disc at posteriorly. Its thickness is not uniform throughout, at the posterior pole it is 0.25 mm. and anteriorly 0.1 mm. in thickness. Its attachment to most of the sclera is loose. There is a potential space in between the sclera and the choroid called suprachoroidal space that is liable to distended by fluid. The separation is more pronounced anteriorly resulting in a ciliochoroidal detachment following trauma and inflammation. The choroid can not be separated at the exit of the vertex veins and round the disc due to firm attachment. The suprachoroidal space extends anteriorly under the ciliary body as supraciliary space. This space is traversed by ciliary vessels and nerves. The ciliary vessels do not give any branch in the suprachoroidal space but the ciliary nerves give fine branches to the outer layer of the choroid.

Histologically the choroid is divided into:

1.Supera choroidal lamina

2.Vascular layer

3.Bruch’s membrane.

1.Suprachoroidal lamina. The suprachoroidal lamina contains melanocytes, fibrocytes and thin fibres. This layer is attached to the choroid on its outer surface, and is attached to the inner surface of the sclera.

2.The vascular layer forms the main bulk of the choroid. It consists of three layers of blood vessels i.e.

(i) The layer of large vessel (ii) The layer of small vessels (iii) The choriocapillaries.

The size of the blood vessels diminish in size from outer surface to the inner surface. The outer layer is mostly venous in nature. The veins unite to form vortex veins which are four in numbers, one in each quadrant. The lower vortex veins are formed by union of choroidal vessels 3 mm behind the equator. Each vortex system unites to form an ampula that drains obliquely through a scleral canal. All the vortex veins drain into ophthalmic veins, there are no valves in choroidal veins7. The spaces in between the vessel is occupied by strands of stroma, melanocytes and fibrocytes like iris and ciliary body. There is no muscle in the choroids.

Choriocapillaries. The choriocapillaries are the largest capillaries in the body. They lie in between the layers of choroidal vessels and Bruch’s membrane. They are channels lined by endothelium in which the choroidal arterioles end. The endothelium is fenestrated in contrast to iris vessels which are non-fenestrated. The choriocapillaries do not anastamose freely, they supply a globular area rather a sector. The choriocapillaries end at ora and rest of the vessels continue in ciliary body. The choriocapillaries are denser and relatively larger under the macula. The main function of the choriocapillaries is to supply nutrients to the outer part of the retina.

3. Bruchi’s membrane. The Bruchi’s membrane is an acellular thin structure that develops from neuro ectoderm as well as uvea. It is thickest around the optic disc. In high magnification, it has five layers. The Bruchi’s membrane forms the blood retinal barrier and acts a filter for metabolic exchange between choriocapillaries and pigment epithelium of the retina8.

The functions of the choroids is to supply blood to the outer retina. Other functions are to keep the interior of the globe dark, to regulate the temperature of the eye and enhance the outflow of aqueous through uveoscleral channel. The choroid does not have any motor function. It is not influenced by parasympathetic nerve. Sympathetic nerve supply regulates choroidal circulation. The choroid is said to act like a lymph node following inflammation.

Blood supply of uvea4, 7

Uvea is a vascular structure, vascularity is maximum in the choroid and least in the iris. The blood supply to the eye ball is from the ophthalmic artery which gives two independent system of blood supply. The retinal system and the ciliary system, the two

generally do not anastomose. The former supplies the inner layer of the retina while the latter supplies the outer layer of the retina, uvea and extra ocular muscles. The ciliary circulation consists of—a posterior ciliary system consisting of long and short posterior ciliary arteries and complex of anterior ciliary arteries.

The long posterior ciliary arteries are two in number. They arise from the opthalmic artery in the orbit, either by a common trunk or two separate trunks. These vessels travel forward to reach the posterior part of the globe. They pierce the sclera one on the lateral side and other on the medial side of the optic nerve in the horizontal plane obliquely to enter the suprachoroidal space. They do not give any branch before reaching the posterior part of the ciliary body. They divide into two branches on entering the ciliary body. The two branches give off multiple smaller twigs, most of which go into the substance of the ciliary body to anastomose with the seven anterior ciliary arteries to form the major arterial circle of the iris that lies just behind the root of the iris in the ciliary body. One of the branches from the main artery passes backward to from the recurrent branch of choroids that supplies the choroid between the oraserrata and the equator.

The posterior ciliary arteries : They also arise from the ophthalmic artery in the orbit as a group of 6 to 8 vessels that divide to form 20 smaller vessels, which travel forward encircling the optic nerve all around. They are more in number on the lateral side to give more blood to the macula. On reaching the choroid these vessels branch profusely. There are two type of vessels in the choroid, a group of shorter vessels that branch and supply the choroid near their entry into the sclera and a group of longer vessels that travel up to the equator to supply the anterior choroid.

The anterior ciliary vessels are continuation of muscular arteries that supply the four recti two for each except the lateral rectus that has only one artery. They also give some branches that are not involved with uveal circulation before perforating the sclera near the limbus and pass through the supraciliary space to end in anterior part of the ciliary body. At this level, they anastomose with the tiny long posterior ciliary arteries to form the major arterial circle. 10 to 12 recurrent branches go backward to supply the anterior choroid.

The iris gets its blood supply from the major circle of iris that also supplies part of the ciliary body and by minor circle of iris that lies just inside the pupillary border and is formed by centripetal branches from major circle of the iris.

Venous drainage of uvea is mostly by vortex veins. The choroid drains via vortex veins exclusively. The iris and ciliary body have two systems of venous drainage-1. A well developed vortex system and 2. A poorly developed ciliary system. The anterior ciliary venous drainage is more developed than the posterior venous drainage.

There are no formed lymphatics in the uvea.

Development of the uvea9, 10, 11

The uvea as a whole has bipartite development. The choroid is dominantly mesodermal except the Bruch’s membrane which is partly mesodermal and partly ectodermal. The iris and the ciliary body are mostly ectodermal in origin except the stroma and the blood vessels.

The ectodermal structure in the iris are the two layers of epithelium, the sphincter, the dilator pupillae and melanocytes.

The epithelium of the ciliary body and the ciliary processes are also ectodermal in origin.

The mesodermal structures in iris and ciliary body are—the iris stroma, blood vessels and ciliary muscles.

The iris and the ciliary body develop from the anterior lip of the optic cup. The edges of the optic cup grow in front of the lens as a double row of epithelium behind the mesoderm. The two layers of the iris epithelium become pigmented in ciliary body. The nonpigmented ciliary epithelium is thrown into folds in which the vessels develop to form the ciliary process. The sphincter muscles starts developing earlier than the dilator, they develops from the non-pigmented iris epithelium surrounding the pupil. The dilator muscles develop from the non pigmented layer near the root.

The mesoderm that lies in front of the developing iris epithelium forms the stroma of the iris. The growth of the iris is influenced by two factors, i.e. Closure of the embryonic fissure (choroidal fissure) and atrophy of tunica vasculosa lentis.

The embryonic (foetal) fissure is a deficiency at the under surface of the optic vesicle and optic stalk extending from the tip of the optic cup almost as far as forebrain. The embryonic fissure is the gap through which the mesoderm surrounding the optic vesicle gets entry into the cavity of the cup and form the retinal and hyaloid system of the vessels. The embryonic fissure starts closing at 10-11 mm. stage at the middle of the fissure and spreads in both directions, the anterior end fuses later than the posterior end. The closure is completed by 18 mm. well before the development of the iris. Failure of the closure of the embryonic fissure results in various congenital anomalies of the uvea ranging from notch coloboma of the iris to extensive coloboma involving all parts of the uvea at the inferior surface of the cup. Non closure of the foetal fissure from end to end leads to formation of colobomatous cystic eye ball.

The choroid develops from mesodermal mass at about 6 mm. A network of capillaries that surround the optic cup develop into choroid. The Bruch’s membrane is secreted by neural epithelial layer. By third month large and medium choroidal vessels develop. The vortex veins also develop at the same time.

Congenital anomalies of the uvea

Congenital anomalies may involve all the three parts of uvea or individually iris, ciliary body and choroids in various combination. Close proximity of iris and ciliary body and choroids to retina may involve them as well. Frequently the congenital anomalies of uvea are due to faulty closure of the foetal fissure resulting into colomboma of the uvea of various types. A coloboma is said to be complete when all the layers of iris, ciliary body or choroids are involved and incomplete where instead of full thickness involvement only partial thickness is underdeveloped. A coloboma is called typical when it develops at the site of the closure of foetal fissure i.e. inferior nasal part of the uvea and atypical when coloboma is located in place away from foetal fissure. The coloboma may be unilateral or bilateral when present in both the eyes they are generally symmetrical. colobomas are generally hereditary, involve both sexes equally.

Coloboma of the iris

Coloboma of the iris may be typical or atypical, can be complete or incomplete.

Involvement of the iris in coloboma varies from a small notch at the pupillary border to extensive

involvement of the uvea from pupillary border to the optic nerve. The typical coloboma is situated at inferionasal part of the iris. It extends from pupillary margin up to the root of the iris, may extend in the ciliary body. The eye may be of normal size but most of the times it is smaller than normal. The pupil is inverted pear shaped or key hole like. If the coloboma extends into the ciliary body, a bluish streak is seen through the conjunctiva. The lower end of the lens is visible with its zonules. If the ciliary body is involved there may be absence of zonules at the site adjacent to the coloboma. There may be localized peripheral lenticular opacity in the lens behind the coloboma. Vision varies from almost normal to severe loss depending upon the degree of involvement of intraocular structures. The eye have variable degrees of errors of refraction.

Psudo polycoria denotes full thickness defects in the substance of iris. The defect is generally circular, looking like additional pupil. Such pupil do not have sphincter or dilator muscles or pigments on its border. These pupil does not react to light or accommodation independent of usual pupil. A similar hole near ciliary body is called iridodiastasis12. A coloboma is called bridge coloboma when a strand of iris tissue spans over a coloboma, bridging the gap, this tissue is mesodermal remnant of pupillary membrane.

No specific treatment is required for coloboma of iris, however, presence of error of refraction should be managed as and when present to prevent amblyopia.

Anomalies of position, size and shape of pupil - Normal pupil is central, circular with slight nasal shift. Position of both the pupil is identical in two eyes. If the pupil is shifted from its normal position it is called ectopia pupil or corectopia . These pupil have their own sphincter and dilator muscles. The two pupil generally do not have symmetrical displacement. The corectopia is generally associated with ectopic lens, the lens generally subluxates away from the decentred pupil.

Congenital microcoria or miotic pupil is due to faulty development of sphincter pupillae. A pupil is said to be microcoria if its diameter is less than 2 mm. in distant gaze.

Anisocoria

When the size of two pupil are different the condition called anisocoria. The two pupils are never of the same size. A change of more than 2 mm. is called clinical anisocoria.

Dyscoria is a rare condition where there is congenital abnormality in shape of pupil other than the coloboma. It is generally bilateral. The pupil is generally slit like in presence of light but becomes almost circular in dim light.

Aniridia13, 13A, 14

Tough the term aniridia should mean total absence of iris, in clinical practice it is not so. Even in most advance cases, there are always some strands of iris present at the roots. In about 50 percent of cases, they obstruct the trabecular mesh work in later life. These strands are generally detected on 360 degrees gonioscopy.13 The condition is present at birth and is bilateral. There are two types of inheritance, 1. Dominant 2. Sporadic.

Besides poor development of the iris the eye has other signs as well. The cornea shows peripheral fine pannus, sensory nystagmus, the pupil is almost as large as the cornea, the lens shows various degrees of opacities on slit lamp examination. The zonules are visible all round and the ciliary process are also seen. The macula is hypo plastic under development of macula is the cause of poor vision and nystagmus.

Secondary glaucoma develops in the second and third decade of life, most probably due to obstruction of trabeculum by iris tags. There may be other causes of glaucoma than simple obstruction of trabecular mesh work. The glaucoma is difficult to manage and the condition does not respond to medical treatment, surgery fails to reach the desired goals unless prophylactic goniotomy is done before onset of glaucoma.13

Half of the sporadic cases may develop Wilm’s tumor. All sporadic cases of aniridia should undergo abdominal examination and to examination by ultrasonography on first presentation and repeated yearly for next few years. Presence of Wilm’s tumor and aniridia is known as Miller’s syndrome.15 Management is difficult, poor vision should be corrected as far as possible and glaucoma controlled as much as possible. The child may require low vision aid and trained as visually handicapped.

Persistent pupillary membrane14, 15, 16

It is an associate anomaly that looks like anomaly of the iris. Persistent pupillary membrane is not a true congenital anomaly of the iris. Persistent pupillary membrane are more common than coloboma of the uvea. It has been reported to be present in 96% of new born, most of which disappears by first year. It persists for few years and then gets absorbed, they are very rare in old age. Persistent pupillary membrane may be unilateral or bilateral and equal in genders. They represent anterior part of tunica vasculosa lentis that supplies nutrition to the lens in foetal life, for the first six month of foetal life and then disappears. Failure of complete disappearance results in shred of mesodermal tissue and obliterated blood vessels that are attached to the collarette. Development of pigment is a post natal feature of the shreds. The strands vary in number and length. They may be gross enough to be seen by oblique illumination without magnification or may be fine enough to be seen by slit lamp. The shreds move freely with the movement of the pupil without restricting it. They normally distort pupillary shape but may be mistaken as posterior synechea which are at pupillary margin. The strands may float freely in the aqueous with one end attachment to the collarette.

It may span the pupil and get attached to the opposite collarette or may cross the pupil in segments. Sometimes it gets attached to the anterior lens capsules where a small opacity may be present. It may get attached to the posterior surface of the cornea with a faint opacity. The condition does not hamper vision or cause any complication hence does not require any treatment.

Coloboma of ciliary body

The isolated congenital coloboma of the ciliary body alone is infrequent. It is generally associated with coloboma of the iris, may be associated with the coloboma of choroids. Commonest congenital anomaly of the ciliary body is typical coloboma due to non-fusion of the foetal fissure in six O’ clock position. However a typical coloboma may be seen at other parts. Coloboma of the ciliary body is most commonly seen in the microphthalmic eyes. It may be associated with subluxation of the lens due to non-development of zonules at the site of the ciliary coloboma.

Colobomata are visualised on indirect opthalmoscopy with scleral indentation. Occasionally it can be seen while doing goneoscopy or ultrasonography. It does not require any treatment.

Coloboma of choroids

Coloboma of choroids can be typical when situated at the site of foetal fissure or atypical when at other than foetal fissure. The former is more common. The coloboma when present are bilateral in two third of the cases. It may extend from the iris to optic nerve and sometimes involving it or it may be localized as a single oval patch in the line of the closure of foetal fissure. There may be more than one such patch in the line of closure of the fissure. Generally a choroidal coloboma has a parabolic appearance with its broader end towards the ciliary body and rounded head towards the optic nerve.

The colour of the coloboma is white due to exposed sclera underneath, the edges are clear cut, sometimes these may be irregular. The edges are pigmented. The retina is absent over the coloboma so it is better to call it a retino choroidal coloboma. The retinal vessels are seen to traverse over this coloboma. The scleral bed is generally depressed, in extreme cases it may be ectatic. In rare instances of bridge coloboma, a patch of retinal tissue may cross the coloboma from side to side. Sometimes the edges of the coloboma may reach very near the macula but not involve it. Vision is generally poor. There is corresponding negative scotoma.

The diagnosis is straight forward.

1.On retinoscopy a white reflex in the lower part amidst a pink glow is seen.

2.Outer margin of the small coloboma is visible with direct opthalmoscopy.

3.The periphery of large coloboma is seen by indirect opthalmoscope that may show up scleral ectasia.

4.Ultrasonography may also show choroidal defect and scleral ectasia.

One of the complications besides sub normal vision is development of rhegmatogenous retinal detachment, when holes may develop at the edge of the coloboma.

Coloboma of macula

Coloboma of the macula may be considered as modified form of atypical choroidal coloboma. It has also been thought to be dysplasia of macula. It is generally bilateral, it may be very small or larger than the optic nerve. The colobomas are punched out horizontally oval areas with clumps of pigments on the periphery and a white floor representing sclera. The area is devoid of choroidal and retinal tissues, rarely abnormal retinal vessel may traverse the gap. The sclera may be ectatic. Vision is greatly reduced leading to nystagmus, squint and amblyopia. A macular coloboma may be mistaken as part of congenital toxoplasmosis.

A large coloboma may give rise to grey reflex on retinoscope. Diagnosis is confirmed by direct and indirect opthomoscopy. An X-ray study is done to exclude intera cranial calcification which is seen in congenital toxoplamosis.

Albinism18

Albinism is hereditary disorder due to abnormal metabolism tyrosine hydroxylase resulting in complete or partial absence of pigment in the body. Clinically albinism has been broadly divided into two types, 1. Oculo cutaneous and 2. Ocular. The former can be divided in biochemically into two sub groups i.e. tyrosinase positive and tyrosinase negative. Oculo cutaneous albinism have extensive systemic as well as ocular involvement. The other group known as tyrosinase positive, have some feature in milder degree of oculcutaneous albinism, it is usually autosomal recessive inheritance.

The ocular albinism is generally X-linked and autosomal recessive in inheritance. This involvement is limited to the globe only.

The oculocutaneous albinism produces fair coloured skin that is sensitive to light. Hair all over the body are light coloured including eye brows and eye lashes.

In ocular albinism the lids, lashes and eye brows are normal. In both the types the eyes are described as red eye because the pupil looks reddish instead of black and the iris is pale blue. The vision is generally greatly reduced. There is nystagmus and squint. The iris may transilluminate at places but there are no holes in the iris. Asymptomatic female carrier of ocular albinism may also have iris trans illumination.19 The eyes generally have various types of errors of refraction, hypermetropia is more common than other types of refractive error. The fundus looks pale against which the retinal and choroidal blood vessels stand out prominently and albinotic fundus is further divided into two types of i.e. with developed macula and without properly differentiated fovea. The eyes with undeveloped macula have congenital colour blindness. In these cases decussation of optic fibers at optic chiasma has also been found to be defective.

Management of albinism is difficult. Vision can rarely be improved, however, full correction should be given to salvage as much of vision as possible, use of tinted glasses reduce glare. Contact lenses are not suitable due to associated nystagmus. Albino children may require low vision aids to pursue studies.

Heterochromia of the uvea

Heterochromia of the uvea is confined to the iris. It can be unilateral, that is one eye has lighter iris than the other. The iris with lighter shade is abnormal. Unilateral heterochromia of iris is called heterochromia iridum. The eyes with different colours are called heterochromia iridus.

The exact cause of congenital heterochromia is not known. Acquired difference is generally due to trauma, inflammation and new growth.

There are many types of heterochromia. Simple heterochromia is common without any other ocular or systemic involvement. Sympathetic heterochromia is seen commonly with

Horner’s syndrome. Complicated heterochromia is seen in Fuch’s heterochromic cyclitis. Some of the systemic anomalies associated with heterochromia of iris are : Waardenburg syndrome, Romber’s syndrome and various types of status dysraphicus.

Simple heterochromia is symptomless and does not require any treatment. Other types may require ocular treatment i.e. Fuch’s heterochromia cyclitis. Systemic conditions require multi system work up and management.

Congenital anomalies of uvea of late onset20

There are some conditions that are thought to be congenital in origin but do not manifest before ten years of age and progress relentlessly towards legal blindness by third or fourth decade. Fortunately they are rare, but neither preventable nor treatable.

They are

1.Gyrate atrophy of choroid

2.Choroideremia

3.Choroidal sclerosis.